How do I change from Classic to Slim?

Skin Editor
1

Inside the Skin Editor, I don’t know where to find this option. I don’t know if it doesn’t have it, but if the options is there please tell me with a screenshot and a mark because I have been trying every option and still can’t find it

2

You can do that here http://minecraft.novaskin.me/resourcepacks#default/assets/minecraft/textures/entity/alex.png

3

You can do that here https://minecraft.novaskin.me/skin/5135753208/AretreBoyCEZCraft